Pirsson and Washington — Geology of New Hampshire. 451 



Mode. — The rock is too coarse-grained to determine the 

 actual mineral composition on ordinary sections by the Rosiwal 

 method with any degree of accuracy, but from measurements 

 made on the hand specimen with a millimeter scale it appears 

 that about 10 per cent of alferric minerals, chiefly hornblende, 

 are present, the remainder being alkalic feldspar with a little 

 quartz. 



Chemical Composition. — The analysis of the specimen gave 

 the result shown in ~No. I of the foregoing table : 



The very small amount of water yielded in the analysis 

 proves that the rock is really in a very fresh and unaltered 

 condition and that the pink color and slight staining are quite 

 superficial. 



For comparison two other analyses of pulaskose are added, 

 one the typical rock from Arkansas and one described by one 

 of us from Montana, and also a phlegrose from Massachusetts. 

 In some ways the rock is closely related to nordmarkose from 

 Norway and the analyses are not very different. The greater 

 amount of lime in the Belknap rock throws it in the domalka- 

 lic rang and the larger relative amount of potash compared 

 with the soda into the sodipotassic subrang, nordmarkose being 

 peralkalic and dosodic. 



Classification. — In the quantitative system the norm is cal- 

 culated to be : 



Quartz 2-04 ") Sal _ 90*88 _ Persal- 



Orthoclase . 35-03 I Fern ~" 8*61 ~~ ' ' ane 



90-88 



O 2'04 



^- = = -0-02. 5, Canadare 



F 87-82 ' ' 



K 2 Q' + Na 2 Q' _ 142 _ Pulas- 



CaO' ~ 41 ~ ' ' kase 



Albite 



41*39 \ 



Anorthite __ 



11-40 



Corundum _ _ 



1-02 



Hyperstbene 



5-30 } 



Magnetite . _ 



2-09 \ 



Umenite 



1-22 ) 



Water 



32 



8-61 



KX>' 63 _ , , 



(I, 5, 2, 3.) 



Total 99-81 



From this table and from what has been stated regarding 

 the fabric and component minerals, the rock should be termed 

 a normative-hornblendic grano-pulaskose. 



The lime-alumina molecules which form anorthite in the 

 norm are divided between the oligoclase-andesine and horn- 

 blende of the mode, but the latter of these minerals is not 

 present in sufficient amount to render the mode abnormative. 

 In the prevailing qualitative systems the rock would be a 

 typical syenite and would belong to the Albany type of Rosen - 

 busch. 



